Stainless steel

ABSTRACT

This invention is for a martensitic, heat hardenable steel of the following composition: CHROMIUM 18 TO 20% MOLYBDENUM 0.2 TO 0.8% CARBON 1.1 TO 1.3% BORON 0 TO 0.2% IRON BALANCE The alloy is preferably heat tempered at a temperature of from 1,000* to 1,200* F. It is characterized by high-wear resistance, corrosion resistance in various media and a freedom from staining. These properties render the steel especially useful for the formation of surgical instruments having a sharp cutting edge.

United States Patent Goldberg 1 Feb. 29, 1972 [54] STAINLESS STEEL [57] ABSTRACT [72] inventor: Robert Goldberg 56 wilshire Drive This invention is foramartensitic, heathardenable steel of the Sharon Mass- 02067 folloying compositionz M- a V. v 7 e [22] Filed: Feb. 10,1969

[21] AppLNo; 798,120

chromium 18 10 20% 1 bd .s% 52 U.S.Cl. ..75/126 c, 148/37, 75/1261 322,13 33:33, [51] Int. Cl. ..C22c 39/14 'P 0 [58] Field of Search ..75/126, 126 C, 126 P; 148/37 mm balance [56} References Cited I I UNITED STATES PATENTS The alloy is preferably heat tempered at a temperature of 2,201,425 5/1942 Berglund.... .....75/126C from l,000 to 1,200F. It is characterized by high wear 2,590,835 4/1952 Kirkby ..75/126C resistance, corrosion resistance in various media and 21 3,250,612 5/1966 Roy ..75/l26P freedom from staining. These properties render the steel 3,469,972 especially useful for the formation of surgical instruments 9/1969 Carlen ..75/ 126 C Primary Examiner-Hyland Bizot Attorney-*Roberts, Cushman and Grover STAINLESS STEEL 1. Field of the Invention This invention relates to martensitic stainless steel and more particularly, to a chromium stainless steel adapted for the formation of surgical instruments requiring a sharp cutting edge.

2. Description of the Prior Art Steels useful for the formation of surgical cutting tools must be characterized by certain properties including high wear resistance which is a function of hardness, corrosion resistance in various media including biological environments and stability and toughness within limits which guarantee an absence of premature staining of the working edge. Chromium stainless steels have been used for the formation of surgical instruments because they are relatively inexpensive, resistant to ordinary corrosive attack, and are capable of being hardened and tempered to desirable strengths.

It is reported in the prior art that heat-treatment affects the corrosion resistance of chromium stainless steels. Heating a hardened steel to temperatures at which carbon precipitates v to form chromium carbides is known to be detrimental to overall corrosion resistance because the formation of such carbides robs the steel of the protective action of chromium. For this reason, it has been customary in the prior art to decrease carbon content to improve the corrosion resistance of steels of a given chromium content. However, this is undesirable as it results in a corresponding reduction in hardness.

DESCRIPTION OF THE INVENTION The martensitic stainless steel of this invention is an improvement over the stainless steels of the prior art in that both chromium content for corrosion resistance and carbon content for hardness are maintained high. The steel has the following formulation:

chromium l8 to 20% molybdenum 0.2 to 0.8% carbon 1.1 to l.3% boron 0 to 0.2% iron balance The above alloy is preferably tempered at a temperature of concentration of chromium andstability and toughness within limits which result in an absence of staining. Though not wishing to be bound by theory, it is believed that the high chromium and carbon contents permissible without loss of corrosion resistance is clue to the molybdenum and in the preferred embodiment, boron, both of which coreact to induce the formation of martensitic phase.

The invention will be further illustrated by the following examples:

The alloys represented in the above two examples are quenched and tempered at a temperature of 1,100 F. followed by slow cooling.

I claim:.

1. A martensitic steel consisting essentially of:

chromium 18 to 20% carbon l.] to li37a molybdenum 0.2 to 0.8% iron balance 2. The composition of claim 1 containing as an additional alloying element up to 0.2 percent boron.

3. The composition of claim 2 where the boron constitutes from 0.1 to 0.2 percent.

4. The steel of claim 1 having the following composition:

chromium l9.5% carbon I 1% molybdenum 0.5% iron balance 5. The steel of claim 4 containing as an additional alloying element 0.1 percent boron.

6. A surgical tool formed from the steel of claim 1. 

2. The composition of claim 1 containing as an additional alloying element up to 0.2 percent boron.
 3. The composition of claim 2 where the boron constitutes from 0.1 to 0.2 percent.
 4. The steel of claim 1 having the following composition: chromium 19.5% carbon 1.2% molybdenum 0.5% iron balance
 5. The steel of claim 4 containing as an additional alloying element 0.1 percent boron.
 6. A surgical tool formed from the steel of claim
 1. 